Process for the production of nodular iron



nited States Patent PROCESS FOR THE PligggCTION-F NODULAR John A.LivingstongNewYorkyN. ApplicationApril 14, .1954, Serial No. 423,145

5 Claims; (Gl."-'15-'-130) This invention relates; to the production .ofcast iron with nodular graphite structure. 7

It has been heretofore known to add magnesium in the form ofcopper-magnesium alloy or nickelmagnesium alloy to the molten cast ironin sufiicient amount to obtain in the melt a magesium addition ofabout-IOJ04%, whereby the final sulphur content willinot-be more thanabout 0.015%. Nickel-magnesium'alloys containing between 10% to 25%magnesium have been used to provide for such addition of magnesium, ascopper-magnesium alloy apparently'had a harmful orinconsistent 'effectonthe production of nodular graphite due to the'presen'ce of copper. Ithas been found that such addition of magnesium influences the productionof cast iron with respect to the carbon, manganese, phosphorous, sulphurand nickel contents and therefore. magnesium was not always suitableinproducing the desired nodular graphite efiect. Lead, antimony, bismuth,arsenic, selenium, tellurium, copper and like elements were found tointerfere with or to be detrimental to the aim of producing nodulargraphite in cast iron.

It has also been known to add substantialamounts of cerium or so calledmischmetal containing to a large amount cerium, to the cast iron melt inorder to obtain nodular cast iron. However, the results obtained werenot always consistent, although cerium apparently acted to 'a certaindegree as a desulphurizer.

The present invention tends to overcome the aforesaid and otherdisadvantages while makinguse of definite advantages inherent intheseall'oys.

It is one of the objects of the present invention to provide meansafiording considerableimprovements in regard to the grain structure andother properties of cast iron and in particuiar in regard to theformation of nodular graphite structure which ensures increased tensilestrength and hardness of the cast.

It is another object of the invention .to provide means causing controlof the sulphur content in cast iron and simultaneously attaining nodulargraphite structures in said cast iron.

Still another object of the present invention is to provide meansavoiding theformati-on of flake graphite or the reversion of nodulargraphite to flake grahpite .in cast iron during productionof the latter.

Yet another object of the invention is toprovide means leading to theelimination of'harmful elements or constituents in cast iron, such astitanium, lead, bismuth, antimony, aluminum, copper and "like residualingredients and to provide further means'acting as powerful carbidestabilizer. v

it is still another object of the invention to'provide means economizingcast iron production and "enabling ready employment of inexpensive rawmaterials regardless of their provenience and their inherent content ofundesirable ingredients, "for obtaining nodular cast iron, whereby anydanger of sulphur segregation in "thecast iron is eliminated.

Still a further objector the invention is to provide '2 means conduciveto the attainment of nodular-cast iron, the melt of which in thepresence of certain combined additives being subjected to deoxidizingand reducing effect,.andfurther to scavenging and purifying action,while the fluidity of the cast iron is prolonged thereby resulting inproducts of denser and improved grain structure.

Still another objectofthe invention residesin the provision of meansaffording the employment of a readily castable and brittle alloy inconnection with consistent production of nodular cast iron, which alloycan be uniformly and easily distributed in the cast iron melt withoutendangering the same through solidification or explosive orvigorousreactions.

A further object of the present invention is to provide means renderingthe possibility of employing a considerable amount of magnesium in analloy charge for obtaining nodular cast iron, whereby the explosive orundesirable reactive "character of magnesium has been eliminated.

Stillaifurther object of the present invention is to provide meanscontributing to the production of nodular cast iron by the employment ofsubstantially pure magnesiumcerium :(mischmetai) alloys, free fromcopper, lead and nickel, whereby the c'astiron melt to which such alloyis added will not be contaminated by ingredients heretofore used as acarrier for cerium and/or'magnesium.

Still another object of the present invention is to provide meansavoiding any marked disturbance in the temperature conditions of theiron melt when magnesiumcerium (mischmetal) alloy isadded to the melt,whereby transformation of cast iron with nodular graphite structure isaccelerated without impairing desirable initial composition of the graycast iron.

Another important object of the present invention is to provide meansredounding to a new nodulizing, economical and bright, stable agent inthe form of an unadulterated alloy which can be readily'produced, bringsabout considerable beneficial results and may be made sufiicientlybrittle to allow crushing thereof and its even distribution in the meltwithout considerable efforts.

In further explaining the nature and underlying prin- 'ciple ofthe'present invention, reference will now be made to exampleshereinafter given, which are typical of the novel gray cast iron madeaccording to the invention.

in making up substantially pure alloys of cerium and magnesium, thecomponents may be melted together. For all practical purposes, thematerial known as mischmetal may be used in place of the pure cerium.Ordinarily, the mischtnetal is figured as 50% cerium in computing theamount to use.

While the magnesium may safely constitute a major proportion of thealloy, it is important to maintain this ingredient at a low enough valueto definitely avoid the danger of explosion in contact with the molteniron. On the other hand, having this safety factor in view as a primaryconsideration, the proportion of cerium must be substantial and may evenexceed magnesium. it is usually desirable to economize in the use ofcerium, mainly on account of its higher cost.

A magnesium-cerium alloy made by combining about 73% magnesium and 27%mischmetal has been successfully used, without showing excessivereactivty. Another alloy which has given even better results, and doesnot exhibit any dangerous properties of magnesium, is made by combiningabout 55% magnesium and 45% mischmetal. The amount of this alloyrequired to effect the conversion of the flake graphite of asample ofgray cast iron to the nodular form was considerably less than any of theother addition agents tried with the possible exception of the straightmischmetal.

Still another safe alloy of magnesium and cerium tried was made up ofabout 43% magnesium and 57% mischmetal. This gave results very similarto those obtained by the alloy composed of 55% magnesium and 45%mischmetal.

The magnesium-cerium alloys of the present invention may advantageouslybe applied to any of the known gray cast irons.

My present invention does not contemplate any particular change in theinoculation treatment or the physical aspects of handling the charge,but is concerned more particularly with the selection of the nodulizingaddition.

An important advantage offered by these magnesiumcerium alloys is theirbrittle nature, which enables them to be very readily disintegrated(granulated) and distributed throughout the molten iron.

The retention of magnesium when using the magnesium-cerium alloy is morecomplete and more consistent than when using magnesium alone. For thisreason, the alloy is more economical to use. Unlike cerium alone, themagnesium-cerium alloy can be satisfactorily used with cast ironcontaining relatively high amounts of sulphur, and the iron need not behypereutectic as to carbon.

Because of their efficiency, the used of magnesiumcerium alloys requiresrelatively small amounts. For example, comparative tests made show thefollowing percentages:

Alloy: Percentage required Copper-magnesium 1V2 Magnesiummischmetal 0.3to 0.5 Ferro-silicon-magnesium 3 An important consideration here is thatthe quantity of magnesium-mischmetal alloy to be added is so small thatthere is little or'no tendency to chill the melt. For a melt of one ton(2,000 lbs.) the following quantities would consequently be required:

Pounds Copper-magnesium 30 Magnesium-mis'chmetal 8Ferro-silicon-magnesium 60 EXAMPLE An alloy of about 45% mischmetal andabout 54% magnesium for producing nodular iron was tested as anodulizing agent in cast iron.

It was found that nodular iron was produced by additions ranging fromabout 0.3 to 0.4% of the above mentioned alloy. This is an advantageover previously tested alloys in that a lower total addition isrequired. The recovery of the magnesium was around 20%. The reactivityof the magnesium on addition to molten iron was considerably reduced byalloying with about 45 mischmetal.

Three induction heats of low phosphorus containing base iron were usedin testing the above alloy. In each heat several ladies were poured andvarying quantities of the alloy crushed to /4 of one inch to V2 of oneinch in size were added to the individual ladles. No molten metal wasthrown from the ladle, although a flare or flash was produced whichquickly subsided. Following the alloy addition the usual 0.4% silicon as75% ferrosilicon was added as the inoculant.

Table I Percent 2 Rec.

Percent E Anal.

Percent Percent 8 Added T.S.X10-= Bhn As Cast-1-.-- 93. 0 212 AsCast-2.--- 84. 0 241 Table II Percent Percent Percent Percent LadleAlloy Mg Mg Mg 0 S1 8 Mn P Added Added Anal. Recov.

Tensile Yielding Elong., Reduct. Brlncll As east Strength Point percentof Area, M. Elast. Hardness X10 X10 percent Table III Percent PercentPercent Percent Ladle Alloy Mg Mg Mg 0 St S Mn P Added Added Anal.Reeov.

Alloy added to ladle 1 at 2600" F. and to ladle 2 at Micrographs showedthat there was little or no pearlitc present. The annealing temperaturelasting approximately one hour was at about 1350 F.

From a comparison of Tables I, II and III it may be readily gatheredthat the alloy here under consideration has the property of producingnodular iron as micrographs have shown and that the physical propertieshave been markedly improved, although a relatively low amount of alloyis required to produce such nodular structure.

The attached drawing shows a chart from which the required alloyaddition for obtaining nodular graphite in a 1" section of iron havingvarying sulphur content is apparent. The chart further clarifies theadditions of various known alloys compared with themischrnetal-magnesium alloy made in accordance with the invention andcontaining approximately magnesium.

It is also to be noted that recent tests further have shown that theemployment of 10 to 73% magnesium with about 90 to 27% mischmetal as anodulizing agent was useful in producing nodular iron, although the highpercentage of mischmetal leads to a rather expensive compound.

It is to be understood that the above description is by way of exampleonly and that various modifications may be made within the scope of theinvention.

This application is a continuation-in-part of application Serial No.155,343, filed April 11, 1950, and now abandoned.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. The process of producing gray cast iron with improved physicalproperties, which consists in adding as a nodulizing agent to said castiron in molten form an alloy which is carrier-free and consists of aboutmagnesium, the remainder being mischmetal.

2. In the process of producing gray cast iron with improved physicalproperties, the step of adding as a nodulizing agent to molten cast ironan allow consisting of magnesium ranging from 10% to about 73%magnesium, the remainder being mischmetal.

3. In the process of manufacturing gray cast iron with improved physicalproperties, the step of adding to said gray cast iron in molten form anodulizing agent magnesium-mischmetal alloy, magnesium being present inthe alloy in an amount of approximately more than 50% and less than 75%,the remainder being solely mischmetal.

4. In the manufacture of a gray cast iron product having carbon innodular form, which consists in adding to a gray cast iron base metal inmolten form a substantially unadulterated magnesium-mischmetal alloyconsisting of about 43% by weight of magnesium and 57% by weight ofmischmetal.

5. The process of manufacturing an improved gray cast iron product whichconsists in adding to a gray cast iron base metal in molten form amagnesium-mischmetal alloy substantially free from any carrier andconsisting of about 73 by weight of magnesium, the remainder beingmisch- 5 metal.

References Cited in the file of this patent UNITED STATES PATENTS 102,622,022 Crome Dec. 16, 1952 FOREIGN PATENTS 263,755 Great Britain Nov.4, 1926 OTHER REFERENCES Chemistry, vol. 5, page 606, edited by Melloi',publ. in 1924 by Longmans, Green and Co., London, England.

1. THE PROCESS FOR PRODUCING GRAY CAST IRON WITH IMPROVED PHYSICALPROPERTIES, WHICH CONSISTS IN ADDING AS A NODULIZING AGENT TO SAID CASTIRON IN MOLTEN FORM AN ALLOY